diff --git a/dom/performance/PerformanceResourceTiming.cpp b/dom/performance/PerformanceResourceTiming.cpp
index c09463965228..f08f320ca729 100644
--- a/dom/performance/PerformanceResourceTiming.cpp
+++ b/dom/performance/PerformanceResourceTiming.cpp
@@ -71,8 +71,22 @@ PerformanceResourceTiming::~PerformanceResourceTiming()
 DOMHighResTimeStamp
 PerformanceResourceTiming::StartTime() const
 {
-  DOMHighResTimeStamp startTime = mTiming->RedirectStartHighRes();
-  return startTime ? startTime : mTiming->FetchStartHighRes();
+  // Force the start time to be the earliest of:
+  //  - RedirectStart
+  //  - WorkerStart
+  //  - AsyncOpen
+  // Ignore zero values.  The RedirectStart and WorkerStart values
+  // can come from earlier redirected channels prior to the AsyncOpen
+  // time being recorded.
+  DOMHighResTimeStamp redirect = mTiming->RedirectStartHighRes();
+  redirect = redirect ? redirect : DBL_MAX;
+
+  DOMHighResTimeStamp worker = mTiming->WorkerStartHighRes();
+  worker = worker ? worker : DBL_MAX;
+
+  DOMHighResTimeStamp asyncOpen = mTiming->AsyncOpenHighRes();
+
+  return std::min(asyncOpen, std::min(redirect, worker));
 }
 
 JSObject*
diff --git a/dom/performance/PerformanceResourceTiming.h b/dom/performance/PerformanceResourceTiming.h
index 2043fd4d4bce..690ed43616c5 100644
--- a/dom/performance/PerformanceResourceTiming.h
+++ b/dom/performance/PerformanceResourceTiming.h
@@ -63,6 +63,12 @@ public:
     mNextHopProtocol = aNextHopProtocol;
   }
 
+  DOMHighResTimeStamp WorkerStart() const {
+    return mTiming && mTiming->TimingAllowed()
+        ? mTiming->WorkerStartHighRes()
+        : 0;
+  }
+
   DOMHighResTimeStamp FetchStart() const {
     return mTiming
         ? mTiming->FetchStartHighRes()
diff --git a/dom/performance/PerformanceTiming.cpp b/dom/performance/PerformanceTiming.cpp
index fa6720a32e50..54e45a80e088 100644
--- a/dom/performance/PerformanceTiming.cpp
+++ b/dom/performance/PerformanceTiming.cpp
@@ -71,6 +71,7 @@ PerformanceTiming::InitializeTimingInfo(nsITimedChannel* aChannel)
 {
   if (aChannel) {
     aChannel->GetAsyncOpen(&mAsyncOpen);
+    aChannel->GetDispatchFetchEventStart(&mWorkerStart);
     aChannel->GetAllRedirectsSameOrigin(&mAllRedirectsSameOrigin);
     aChannel->GetRedirectCount(&mRedirectCount);
     aChannel->GetRedirectStart(&mRedirectStart);
@@ -86,30 +87,38 @@ PerformanceTiming::InitializeTimingInfo(nsITimedChannel* aChannel)
     aChannel->GetResponseEnd(&mResponseEnd);
     aChannel->GetCacheReadEnd(&mCacheReadEnd);
 
-    // the performance timing api essentially requires that the event timestamps
-    // are >= asyncOpen().. but in truth the browser engages in a number of
-    // speculative activities that sometimes mean connections and lookups begin
-    // earlier. Workaround that here by just using asyncOpen as the minimum
-    // timestamp for dns and connection info.
+    // The performance timing api essentially requires that the event timestamps
+    // have a strict relation with each other. The truth, however, is the browser
+    // engages in a number of speculative activities that sometimes mean connections
+    // and lookups begin at different times. Workaround that here by clamping
+    // these values to what we expect FetchStart to be.  This means the later of
+    // AsyncOpen or WorkerStart times.
     if (!mAsyncOpen.IsNull()) {
-      if (!mDomainLookupStart.IsNull() && mDomainLookupStart < mAsyncOpen) {
-        mDomainLookupStart = mAsyncOpen;
+      // We want to clamp to the expected FetchStart value.  This is later of
+      // the AsyncOpen and WorkerStart values.
+      const TimeStamp* clampTime = &mAsyncOpen;
+      if (!mWorkerStart.IsNull() && mWorkerStart > mAsyncOpen) {
+        clampTime = &mWorkerStart;
       }
 
-      if (!mDomainLookupEnd.IsNull() && mDomainLookupEnd < mAsyncOpen) {
-        mDomainLookupEnd = mAsyncOpen;
+      if (!mDomainLookupStart.IsNull() && mDomainLookupStart < *clampTime) {
+        mDomainLookupStart = *clampTime;
       }
 
-      if (!mConnectStart.IsNull() && mConnectStart < mAsyncOpen) {
-        mConnectStart = mAsyncOpen;
+      if (!mDomainLookupEnd.IsNull() && mDomainLookupEnd < *clampTime) {
+        mDomainLookupEnd = *clampTime;
       }
 
-      if (!mSecureConnectionStart.IsNull() && mSecureConnectionStart < mAsyncOpen) {
-        mSecureConnectionStart = mAsyncOpen;
+      if (!mConnectStart.IsNull() && mConnectStart < *clampTime) {
+        mConnectStart = *clampTime;
       }
 
-      if (!mConnectEnd.IsNull() && mConnectEnd < mAsyncOpen) {
-        mConnectEnd = mAsyncOpen;
+      if (!mSecureConnectionStart.IsNull() && mSecureConnectionStart < *clampTime) {
+        mSecureConnectionStart = *clampTime;
+      }
+
+      if (!mConnectEnd.IsNull() && mConnectEnd < *clampTime) {
+        mConnectEnd = *clampTime;
       }
     }
   }
@@ -129,9 +138,13 @@ PerformanceTiming::FetchStartHighRes()
     }
     MOZ_ASSERT(!mAsyncOpen.IsNull(), "The fetch start time stamp should always be "
         "valid if the performance timing is enabled");
-    mFetchStart = (!mAsyncOpen.IsNull())
-        ? TimeStampToDOMHighRes(mAsyncOpen)
-        : 0.0;
+    if (!mAsyncOpen.IsNull()) {
+      if (!mWorkerStart.IsNull() && mWorkerStart > mAsyncOpen) {
+        mFetchStart = TimeStampToDOMHighRes(mWorkerStart);
+      } else {
+        mFetchStart = TimeStampToDOMHighRes(mAsyncOpen);
+      }
+    }
   }
   return mFetchStart;
 }
@@ -205,6 +218,26 @@ PerformanceTiming::ShouldReportCrossOriginRedirect() const
   return (mRedirectCount != 0) && mReportCrossOriginRedirect;
 }
 
+DOMHighResTimeStamp
+PerformanceTiming::AsyncOpenHighRes()
+{
+  if (!nsContentUtils::IsPerformanceTimingEnabled() || !IsInitialized() ||
+      nsContentUtils::ShouldResistFingerprinting() || mAsyncOpen.IsNull()) {
+    return mZeroTime;
+  }
+  return TimeStampToDOMHighRes(mAsyncOpen);
+}
+
+DOMHighResTimeStamp
+PerformanceTiming::WorkerStartHighRes()
+{
+  if (!nsContentUtils::IsPerformanceTimingEnabled() || !IsInitialized() ||
+      nsContentUtils::ShouldResistFingerprinting() || mWorkerStart.IsNull()) {
+    return mZeroTime;
+  }
+  return TimeStampToDOMHighRes(mWorkerStart);
+}
+
 /**
  * RedirectStartHighRes() is used by both the navigation timing and the
  * resource timing. Since, navigation timing and resource timing check and
diff --git a/dom/performance/PerformanceTiming.h b/dom/performance/PerformanceTiming.h
index c104370de788..729b980279d9 100644
--- a/dom/performance/PerformanceTiming.h
+++ b/dom/performance/PerformanceTiming.h
@@ -157,7 +157,12 @@ public:
   // the timing-allow-origin check in HttpBaseChannel::TimingAllowCheck
   bool ShouldReportCrossOriginRedirect() const;
 
+  // The last channel's AsyncOpen time.  This may occur before the FetchStart
+  // in some cases.
+  DOMHighResTimeStamp AsyncOpenHighRes();
+
   // High resolution (used by resource timing)
+  DOMHighResTimeStamp WorkerStartHighRes();
   DOMHighResTimeStamp FetchStartHighRes();
   DOMHighResTimeStamp RedirectStartHighRes();
   DOMHighResTimeStamp RedirectEndHighRes();
@@ -273,6 +278,7 @@ private:
   DOMHighResTimeStamp mZeroTime;
 
   TimeStamp mAsyncOpen;
+  TimeStamp mWorkerStart;
   TimeStamp mRedirectStart;
   TimeStamp mRedirectEnd;
   TimeStamp mDomainLookupStart;
diff --git a/dom/webidl/PerformanceResourceTiming.webidl b/dom/webidl/PerformanceResourceTiming.webidl
index 021b84ae2ce8..112228325a1f 100644
--- a/dom/webidl/PerformanceResourceTiming.webidl
+++ b/dom/webidl/PerformanceResourceTiming.webidl
@@ -4,7 +4,7 @@
  * You can obtain one at http://mozilla.org/MPL/2.0/.
  *
  * The origin of this IDL file is
- * http://w3c-test.org/webperf/specs/ResourceTiming/#performanceresourcetiming
+ * https://w3c.github.io/resource-timing/#performanceresourcetiming
  *
  * Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C
  * liability, trademark and document use rules apply.
@@ -12,14 +12,10 @@
 
 interface PerformanceResourceTiming : PerformanceEntry
 {
-  // A string with the name of that element that initiated the load.
-  // If the initiator is a CSS resource, the initiatorType attribute must return
-  // the string "css".
-  // If the initiator is an XMLHttpRequest object, the initiatorType attribute
-  // must return the string "xmlhttprequest".
   readonly attribute DOMString initiatorType;
   readonly attribute DOMString nextHopProtocol;
 
+  readonly attribute DOMHighResTimeStamp workerStart;
   readonly attribute DOMHighResTimeStamp redirectStart;
   readonly attribute DOMHighResTimeStamp redirectEnd;
   readonly attribute DOMHighResTimeStamp fetchStart;